Pottawatomie County was created by the Kansas Territorial legislature in 1857, out of land formerly included in Riley County. The present county seat of Westmoreland was selected by a vote held in 1882.

Pottawatomie County was a prohibition, or "dry", county until the Kansas Constitution was amended in 1986 and voters approved the sale of alcoholic liquor by the individual drink with a 30% food sales requirement.[3]

There were 6,771 households out of which 36.40% had children under the age of 18 living with them, 62.40% were married couples living together, 7.20% had a female householder with no husband present, and 27.20% were non-families. 23.20% of all households were made up of individuals and 9.70% had someone living alone who was 65 years of age or older. The average household size was 2.65 and the average family size was 3.15.

In the county the population was spread out with 29.50% under the age of 18, 7.70% from 18 to 24, 27.70% from 25 to 44, 21.60% from 45 to 64, and 13.50% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 98.00 males. For every 100 females age 18 and over, there were 96.70 males.

The median income for a household in the county was $40,176, and the median income for a family was $47,261. Males had a median income of $31,368 versus $23,238 for females. The per capita income for the county was $17,785. About 6.40% of families and 9.70% of the population were below the poverty line, including 14.10% of those under age 18 and 10.30% of those age 65 or over.

Pottawatomie County is divided into twenty-three townships. The city of Manhattan is considered governmentally independent and is excluded from the census figures for the townships. In the following table, the population center is the largest city (or cities) included in that township's population total, if it is of a significant size.